I don't see why this long, boring, tedious cap is going on. I want to settle this once and for all. Go to Wookieepedia.com, the Star Wars Wiki. Search for TFU II. It specifically states that Vader took his dead body to Kamino, cloned him, and the clone gets "residual genetic memories" from his original self. He hijacks Vader's TIE fighter, and escapes to Cato Neimoidia, where Kota is executed in a gladitorial match like the Colusieum fight at the end of Episode II. That is why the "arena" in the trailer is shown, it is not The Netherworld!!!

There is no resurrection, there is no concealment of his death, nor is there playing as him in the Netherworld, or anything else! There is only the clone.